The transmission of multimedia data, as in the applications of video conferencing, digital library, home shopping and distance learning, has been an important task for researchers either in the industrial or in the academic field. Both audio and video data are transmitted over high-speed networks in these applications and played back continuously at remote client equipments. As resources are usually allocated exclusively to a fixed-size to each service stream, it is relatively simple for networks to support CBR services in terms of management complexity and overhead. However, due to compression technologies, digital media streams (e.g., audio and video data streams) are usually tranmitted with VBR. It would be a waste of the network bandwidth if the peak rate is allocated in transmitting VBR streams because the average rate of the VBR streams, e.g., an MPEG video, is less than 25% of its peak rate.
On the other hand, in the VBR service model, data streams are multiplexed to share the entire linkage bandwidth. The admission control and the network transmission scheduling at the intermediate network nodes, e.g., output ports of ATM switches, are usually quite complicated both in the analysis and in the implementation.
FIG. 1 illustrates the system schematics of a data transmission system which transmits information data through a network. As shown in the figure, a data transmission system includes a network main frame 1, at least one server site 20 and at least one client site 30. At the server site 20, at least one retrieval scheduler 21, a server buffer 22 and a transmission scheduler 23 are equipped. On the other hand, at the client site 30, a multimedia display 31, a playback scheduler 32 and a client buffer 33 are equipped. This figure illustrates the structure of a data transmission system facilitating the description of the present invention and will be taken for reference in the following description.
In the conventional art, a deterministic bounding interval dependent traffic model (D-BIND traffic model) has been disclosed. (See Zhang and Knightly: "A new approach to support delay-sensitive VBR video in packet-switched networks", Proc. 5th Workshop on Network and Operating Systems Support for Digital Audio and Video, 1995.) This approach models VBR traffic based on the interdependence among a plurality of bounded regions. However, the required buffer size is large.
Another deterministic guaranteed service called constant-rate transmission and transport (CRTT) was disclosed by McManus and Ross. (McManus and Ross: "Video on demand over ATM: Constant-rate transmission and transport", Proc. IEEE INFOCOM, March 1996.) In this approach, a CRTT server transmits information data to a client at a constant rate. The client starts to playback the first frame of the information data after having received a certain amount of data (also called "build up"). By choosing an appropriate transmission rate, which is a constant rate, and the build up size, the client buffer size can be minimized. The drawback of this approach, however, is that the size of the client buffer will be relatively large. It requires approximately 22.3 MB memory to playback the data of the famous movie: "Star Wars".
It is thus a need in the industry to provide a novel method for the transmission of VBR information data over CBR channels whereby the buffer size and the working-ahead as required may be minimized. It is also necessary to provide a method for the transmission of VBR information data over CBR channels whereby the network utilization may be maximized.